linux-kernel - Re: [PATCH 1/2] protect /sbin/init from unwanted signals more

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Date:	Thu, 20 Nov 2008 21:00:50 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] protect /sbin/init from unwanted signals more

On 11/20, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> > On 11/19, Eric W. Biederman wrote:
> >>
> >> Roland McGrath <roland@...hat.com> writes:
> >>
> >> > With that, I wonder if the SIGNAL_UNKILLABLE checks in get_signal_to_deliver
> >> > and complete_signal are needed at all.  Hmm, I guess we do because this
> >> > doesn't affect blocked signals, so they might be unblocked and delivered.
> >> > (Note that since it doesn't affect blocked signals, this doesn't break init
> >> > using sigwait if it wanted to.)
> >>
> >> Ah.  That answers the question I had bouncing in the back of my head.
> >
> > Even worse. The signal can be dequeued even before unblocked by the target.
> > complete_signal() can "redirect" this signal to another thread wich doesn't
> > block it.
>
> The signal handlers should still be the same.

Yes sure. and the handler can be SIG_DFL.

In short, if we have any reason (we do have) to check sig_kernel_ignore()
in get_signal_to_deliver(), then we have the same reason to check
SIGNAL_UNKILLABLE too.

> >> Which reminds me.  I need to retest, but I had a case where I had a trivial
> > init
> >> that set all signal handlers to SIG_IGN so it could ignore SIGCHLD.  And not
> >> all of it's children were getting reaped automagically.  Do we have a bug in
> >> the reparenting/reaping logic?
> >
> > Ah... I thought this was already fixed... shouldn't reparent_thread()
> > check task_detached() after do_notify() ? like ptrace_exit() does.
>
> Like I said I need to retest.  I was on a 2.6.26 fedora kernel base.
> So if there have been recent bug fixes things may have changed.

I bet the bug is still here.

The fix should be simple, except we can't trust ptrace_reparented().

I'll send the patch, but first I'd like to do another one. Since
I stopped my attempts to understand the orphaned pgrps a long
ago, I hope you can review ;)

Oleg.

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